Saturday, October 18, 2014

Wooden clock wheel blanks

I've been fascinated by mechanical clocks, and have wanted to build one.  Since wood is my usual medium, it seemed appropriate to try...  I have made several attempts at building escapements, and had some limited success, but each time learning...  So I decided that I should build a gear train, to see how that goes.

It is set up so that the wheels are configured as follows:

Escape wheel: 15 teeth, rotates 4 times per minute
Escape pinion: 6 teeth
Fourth wheel: 30 teeth
Fourth pinion: 6 teeth
Third wheel: 36 teeth
Third pinion: 6 teeth
Center wheel: 48 teeth (rotates once per hour)

In order to ensure each gear is clear of the next arbor, I did a little side calculation.

I set the size of the center wheel so that it fit on a 8.5" x 11" sheet of paper, and drew the center wheel in Inkscape and also the third and fourth wheels.  I forgot to draw the spokes, though.

Once printed, I affixed the patterns to some 1/2" birch plywood.  I use Elmer's Glue-All, spread very thinly with a sponge brush.  If the glue is too thick, the pattern will wrinkle.  Once the glue is spread, place the pattern down, and rub from the center out to remove air bubbles.  Let dry completely before cutting out roughly.

After cutting the wheels out roughly, I cut the outer circles of each wheel on the scroll saw.  Since I didn't mark an outer circle on the pinions (I should have), I just cut them completely.

With the outer circles present, it's easy to center the wheel blanks in the chuck of the lathe, so that the center hole can be drilled accurately.
The since the pinions have six leaves and my lathe chuck has three jaws, I was able to grip each pinion accurately for center drilling also.
Once drilled, I traced out the spokes (should remember to put them on the pattern next time), and drilled each so that the scroll saw blade fits through.

After cutting the spokes, the blanks are complete!